SYNOPSIS

DESCRIPTION

The
utility selectively processes conditional
cpp(1)
directives.
It removes from a file
both the directives
and any additional text that they specify should be removed,
while otherwise leaving the file alone.

The
utility acts on
#if , #ifdef , #ifndef#elif , #else
and
#endif
lines,
using macros specified in
-D
and
-U
command line options or in
-f
definitions files.
A directive is processed
if the macro specifications are sufficient to provide
a definite value for its control expression.
If the result is false,
the directive and the following lines under its control are removed.
If the result is true,
only the directive is removed.
An
#ifdef
or
#ifndef
directive is passed through unchanged
if its controlling macro is not specified.
Any
#if
or
#elif
control expression that has an unknown value or that
cannot parse is passed through unchanged.
By default,
ignores
#if
and
#elif
lines with constant expressions;
it can be told to process them by specifying the
-k
flag on the command line.

It understands a commonly-used subset
of the expression syntax for
#if
and
#elif
lines:
integer constants,
integer values of macros defined on the command line,
the
Fn defined
operator,
the operators
! , < , ><= , >= , == , !=&& , ||
and parenthesized expressions.
A kind of
``short circuit''
evaluation is used for the
&&
operator:
if either operand is definitely false then the result is false,
even if the value of the other operand is unknown.
Similarly,
if either operand of
||
is definitely true then the result is true.

When evaluating an expression,
does not expand macros first.
The value of a macro must be a simple number,
not an expression.
A limited form of indirection is allowed,
where one macro's value is the name of another.

In most cases,
does not distinguish between object-like macros
(without arguments) and function-like macros (with arguments).
A function-like macro invocation can appear in
#if
and
#elif
control expressions.
If the macro is not explicitly defined,
or is defined with the
-D
flag on the command-line,
or with
#define
in a
-f
definitions file,
its arguments are ignored.
If a macro is explicitly undefined on the command line with the
-U
flag,
or with
#undef
in a
-f
definitions file,
it may not have any arguments since this leads to a syntax error.

The
utility understands just enough about C
to know when one of the directives is inactive
because it is inside
a comment,
or affected by a backslash-continued line.
It spots unusually-formatted preprocessor directives
and knows when the layout is too odd for it to handle.

A script called
unifdefall
can be used to remove all conditional
cpp(1)
directives from a file.
It uses
-s
and
cpp -dM
to get lists of all the controlling macros
and their definitions (or lack thereof),
then invokes
with appropriate arguments to process the file.

OPTIONS

-D sym = val

Specify that a macro is defined to a given value.

-D sym

Specify that a macro is defined to the value 1.

-U sym

Specify that a macro is undefined.

If the same macro appears in more than one argument,
the last occurrence dominates.

-iD sym [= val
]

-iU sym

C strings, comments,
and line continuations
are ignored within
#ifdef
and
#ifndef
blocks
controlled by macros
specified with these options.

-f defile

The file
defile
contains
#define
and
#undef
preprocessor directives,
which have the same effect as the corresponding
-D
and
-U
command-line arguments.
You can have multiple
-f
arguments and mix them with
-D
and
-U
arguments;
later options override earlier ones.

Each directive must be on a single line.
Object-like macro definitions (without arguments)
are set to the given value.
Function-like macro definitions (with arguments)
are treated as if they are set to 1.

Compress blank lines around a deleted section.
Mutually exclusive with the
-b
option.

-c

Complement,
i.e., lines that would have been removed or blanked
are retained and vice versa.

-d

Turn on printing of debugging messages.

-e

By default,
will report an error if it needs to remove
a preprocessor directive that spans more than one line,
for example, if it has a multi-line
comment hanging off its right hand end.
The
-e
flag makes it ignore the line instead.

-h

Print help.

-I path

Specifies to
unifdefall
an additional place to look for
#include
files.
This option is ignored by
for compatibility with
cpp(1)
and to simplify the implementation of
unifdefall

-K

Always treat the result of
&&
and
||
operators as unknown if either operand is unknown,
instead of short-circuiting when unknown operands can't affect the result.
This option is for compatibility with older versions of
.

-k

Process
#if
and
#elif
lines with constant expressions.
By default, sections controlled by such lines are passed through unchanged
because they typically start
``#if 0
''
and are used as a kind of comment to sketch out future or past development.
It would be rude to strip them out, just as it would be for normal comments.

-m

Modify one or more input files in place.

-M backext

Modify input files in place, and keep backups of the original files by
appending the
backext
to the input filenames.

-n

Add
#line
directives to the output following any deleted lines,
so that errors produced when compiling the output file correspond to
line numbers in the input file.

-o outfile

Write output to the file
outfile
instead of the standard output when processing a single file.

-s

Instead of processing an input file as usual,
this option causes
to produce a list of macros that are used in
preprocessor directive controlling expressions.

-S

Like the
-s
option, but the nesting depth of each macro is also printed.
This is useful for working out the number of possible combinations
of interdependent defined/undefined macros.

-t

Disables parsing for C strings, comments,
and line continuations,
which is useful
for plain text.
This is a blanket version of the
-iD
and
-iU
flags.

-V

Print version details.

-x Bro 012 Brc

Set exit status mode to zero, one, or two.
See the
Sx EXIT STATUS
section below for details.

The
utility takes its input from
stdin
if there are no
file
arguments.
You must use the
-m
or
-M
options if there are multiple input files.
You can specify inut from stdin or output to stdout with
`-'